1. Field of the Invention
The present invention relates to an image forming apparatus, such as a color copier, which can read a color document and transmit corresponding document image data to an external device via a communication network.
2. Description of the Related Art
In the case where copying is performed on a color copier, R (red), G (green) and B (blue) data of a document scanned by a scanner are converted by a color conversion section to Y (yellow), M (magenta), C (cyan) and K (black) data with the use of various kinds of image processing parameters. Color printing is carried out on a printing section having a plurality of process units for forming an image of respective colors with the use of the YMCK data. The respective process units include a photosensitive drum, a light exposure unit, a developing unit, and so on. At the time of printing, in order to prevent an image of respective colors from being displaced on a sheet due to each interval between the process units of respective colors, the image data of respective colors are supplied to the process units while being delayed by a corresponding different time.
The color copier generally has the function of preventing the forgery of bank notes, negotiable securities and so on. In order to detect a given printed matter, such as the bank notes and negotiable securities (hereinafter referred to as a specific document), such a type of color copier has a specific document detecting section. When copying is made on the color copier, the document image data scanned by the scanner is checked by the specific document detecting section. If, therefore, the document image is recognized as being a specific document image, the image data delayed as set out above is converted to different data other than the image data and sent to the printing section. Therefore, it is possible to prevent the specific data from being printed normally.
Recently, a copier has been widely adopted which can be used as a network scanner. In the case where the copier is used as such a network scanner, a document image is scanned by the scanner of the copier and, without being color-converted, the scanned RGB image data is transmitted through a printer controller of the copier to an external unit such as a personal computer, connected via the communication network.
In the case where the copier is used as the network scanner, the image data is transmitted through the printer controller to the external device without being delayed. Even if, therefore, the specific document detecting section recognizes the document which has been scanned by the scanner as being the specific document and the image data which is supplied to the printer controller are changed to other data, the specific document image will be transmitted to some extent to the external device through the printer controller.
In the case where, therefore, the copier is used as the network scanner, checking is made, by prescanning, whether or not the document is the specific document and an image read out by the main scanning is output to the printer controller. Further, the image data scanned at the time of prescanning is not output to the printer controller. If the document image is recognized as being the specific document by the prescanning, the image processing parameters used in the image processing section at the time of main scanning are changed and different data other than the document image are output to the printer controller.
As set out above, in the case where the copier is used as a network scanner, the checking is made by prescanning whether or not the document is a specific document and the change of the image processing parameters is made in a time interval between the checking of the specific document by prescanning and the starting of main scanning.
In the case where, however, a normal document is set on the document glass at the time of prescanning and it is replaced by the specific document at the time of main scanning, there is sometimes a case where part of the specific document is read as a normal image, output to the printer controller and further forwarded to the external device. At this time it may be considered that the specific document is read from various directions and positions and the corresponding imperfect images obtained at this time are synthesized with the use of an image processing technique. Therefore, it is not possible to prevent a forgery sufficiently in a conventional color copier.